Pectoralis major muscle

The pectoralis major is a thick, fan-shaped muscle, on the chest (front) of the human body.

Muscles on top of the chest and front of the arm

It makes up most of the chest muscles, and is under the breast. In sports as well as bodybuilding, the pectoral muscles may be referred to as "pecs", "pectoral muscle" or "chest muscle" because it is the larger surface muscle in the chest area.